@RequestParam @RequestBody @PathVariable 等参数绑定注解详解
引言：
接上一篇文章，对@RequestMapping进行地址映射讲解之后，该篇主要讲解request 数据到handler method 参数数据的绑定所用到的注解和什么情形下使用；
简介：
handler method 参数绑定常用的注解,我们根据他们处理的Request的不同内容部分分为四类：（主要讲解常用类型）
A、处理requet uri 部分（这里指uri template中variable，不含queryString部分）的注解： @PathVariable;
B、处理request header部分的注解： @RequestHeader, @CookieValue;
C、处理request body部分的注解：@RequestParam, @RequestBody;
D、处理attribute类型是注解： @SessionAttributes, @ModelAttribute;
1、 @PathVariable
当使用@RequestMapping URI template 样式映射时， 即 someUrl/{paramId}, 这时的paramId可通过 @Pathvariable注解绑定它传过来的值到方法的参数上。
示例代码：
- @Controller
- @RequestMapping("/owners/{ownerId}")
- public class RelativePathUriTemplateController {
- @RequestMapping("/pets/{petId}")
- public void findPet(@PathVariable String ownerId,@PathVariable String petId, Model model) {
- // implementation omitted
- }
- }
@Controller
@RequestMapping("/owners/{ownerId}")
public class RelativePathUriTemplateController {
@RequestMapping("/pets/{petId}")
public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {
// implementation omitted
}
}2、 @RequestHeader、@CookieValue
@RequestHeader 注解，可以把Request请求header部分的值绑定到方法的参数上。
示例代码：
这是一个Request 的header部分：
- Host localhost:8080
- Accept text/html,application/xhtml+xml,application/xml;q=0.9
- Accept-Language fr,en-gb;q=0.7,en;q=0.3
- Accept-Encoding gzip,deflate
- Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7
- Keep-Alive 300
Host localhost:8080
Accept text/html,application/xhtml+xml,application/xml;q=0.9
Accept-Language fr,en-gb;q=0.7,en;q=0.3
Accept-Encoding gzip,deflate
Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive 300- @RequestMapping("/displayHeaderInfo.do")
- public void displayHeaderInfo(@RequestHeader("Accept-Encoding") String encoding,
- @RequestHeader("Keep-Alive")long keepAlive) {
- //...
- }
@RequestMapping("/displayHeaderInfo.do")
public void displayHeaderInfo(@RequestHeader("Accept-Encoding") String encoding,
@RequestHeader("Keep-Alive") long keepAlive) {
//...
}
@CookieValue 可以把Request header中关于cookie的值绑定到方法的参数上。
例如有如下Cookie值：
- JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84
JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84- @RequestMapping("/displayHeaderInfo.do")
- public void displayHeaderInfo(@CookieValue("JSESSIONID") String cookie) {
- //...
- }
@RequestMapping("/displayHeaderInfo.do")
public void displayHeaderInfo(@CookieValue("JSESSIONID") String cookie) {
//...
}
3、@RequestParam, @RequestBody
@RequestParam
A） 常用来处理简单类型的绑定，通过Request.getParameter() 获取的String可直接转换为简单类型的情况（ String--> 简单类型的转换操作由ConversionService配置的转换器来完成）；因为使用request.getParameter()方式获取参数，所以可以处理get 方式中queryString的值，也可以处理post方式中 body data的值；
B）用来处理Content-Type: 为 application/x-www-form-urlencoded编码的内容，提交方式GET、POST；
C) 该注解有两个属性： value、required； value用来指定要传入值的id名称，required用来指示参数是否必须绑定；
示例代码：
- @Controller
- @RequestMapping("/pets")
- @SessionAttributes("pet")
- public class EditPetForm {
- // ...
- @RequestMapping(method = RequestMethod.GET)
- public String setupForm(@RequestParam("petId")int petId, ModelMap model) {
- Pet pet = this.clinic.loadPet(petId);
- model.addAttribute("pet", pet);
- return "petForm";
- }
- // ...
@Controller
@RequestMapping("/pets")
@SessionAttributes("pet")
public class EditPetForm {
// ...
@RequestMapping(method = RequestMethod.GET)
public String setupForm(@RequestParam("petId") int petId, ModelMap model) {
Pet pet = this.clinic.loadPet(petId);
model.addAttribute("pet", pet);
return "petForm";
}
// ...@RequestBody
该注解常用来处理Content-Type: 不是application/x-www-form-urlencoded编码的内容，例如application/json, application/xml等；
它是通过使用HandlerAdapter 配置的HttpMessageConverters来解析post data body，然后绑定到相应的bean上的。
因为配置有FormHttpMessageConverter，所以也可以用来处理 application/x-www-form-urlencoded的内容，处理完的结果放在一个MultiValueMap
示例代码：
- @RequestMapping(value ="/something", method = RequestMethod.PUT)
- public void handle(@RequestBody String body, Writer writer)throws IOException {
- writer.write(body);
- }
@RequestMapping(value = "/something", method = RequestMethod.PUT)
public void handle(@RequestBody String body, Writer writer) throws IOException {
writer.write(body);
}4、@SessionAttributes, @ModelAttribute
@SessionAttributes:
该注解用来绑定HttpSession中的attribute对象的值，便于在方法中的参数里使用。
该注解有value、types两个属性，可以通过名字和类型指定要使用的attribute 对象；
示例代码：
- @Controller
- @RequestMapping("/editPet.do")
- @SessionAttributes("pet")
- public class EditPetForm {
- // ...
- }
@Controller
@RequestMapping("/editPet.do")
@SessionAttributes("pet")
public class EditPetForm {
// ...
}@ModelAttribute
该注解有两个用法，一个是用于方法上，一个是用于参数上；
用于方法上时： 通常用来在处理@RequestMapping之前，为请求绑定需要从后台查询的model；
用于参数上时： 用来通过名称对应，把相应名称的值绑定到注解的参数bean上；要绑定的值来源于：
A） @SessionAttributes 启用的attribute 对象上；
B） @ModelAttribute 用于方法上时指定的model对象；
C） 上述两种情况都没有时，new一个需要绑定的bean对象，然后把request中按名称对应的方式把值绑定到bean中。
用到方法上@ModelAttribute的示例代码：
- // Add one attribute
- // The return value of the method is added to the model under the name "account"
- // You can customize the name via @ModelAttribute("myAccount")
- @ModelAttribute
- public Account addAccount(@RequestParam String number) {
- return accountManager.findAccount(number);
- }
// Add one attribute
// The return value of the method is added to the model under the name "account"
// You can customize the name via @ModelAttribute("myAccount")
@ModelAttribute
public Account addAccount(@RequestParam String number) {
return accountManager.findAccount(number);
}
这种方式实际的效果就是在调用@RequestMapping的方法之前，为request对象的model里put（“account”， Account）；
用在参数上的@ModelAttribute示例代码：
- @RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)
- public String processSubmit(@ModelAttribute Pet pet) {
- }
@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)
public String processSubmit(@ModelAttribute Pet pet) {
}补充讲解：
问题： 在不给定注解的情况下，参数是怎样绑定的？
通过分析AnnotationMethodHandlerAdapter和RequestMappingHandlerAdapter的源代码发现，方法的参数在不给定参数的情况下：
若要绑定的对象时简单类型： 调用@RequestParam来处理的。
若要绑定的对象时复杂类型： 调用@ModelAttribute来处理的。
这里的简单类型指java的原始类型(boolean, int 等)、原始类型对象（Boolean, Int等）、String、Date等ConversionService里可以直接String转换成目标对象的类型；
下面贴出AnnotationMethodHandlerAdapter中绑定参数的部分源代码：
- private Object[] resolveHandlerArguments(Method handlerMethod, Object handler,
- NativeWebRequest webRequest, ExtendedModelMap implicitModel)throws Exception {
- Class[] paramTypes = handlerMethod.getParameterTypes();
- Object[] args = new Object[paramTypes.length];
- for (int i =0; i < args.length; i++) {
- MethodParameter methodParam = new MethodParameter(handlerMethod, i);
- methodParam.initParameterNameDiscovery(this.parameterNameDiscoverer);
- GenericTypeResolver.resolveParameterType(methodParam, handler.getClass());
- String paramName = null;
- String headerName = null;
- boolean requestBodyFound =false;
- String cookieName = null;
- String pathVarName = null;
- String attrName = null;
- boolean required =false;
- String defaultValue = null;
- boolean validate =false;
- Object[] validationHints = null;
- int annotationsFound =0;
- Annotation[] paramAnns = methodParam.getParameterAnnotations();
- for (Annotation paramAnn : paramAnns) {
- if (RequestParam.class.isInstance(paramAnn)) {
- RequestParam requestParam = (RequestParam) paramAnn;
- paramName = requestParam.value();
- required = requestParam.required();
- defaultValue = parseDefaultValueAttribute(requestParam.defaultValue());
- annotationsFound++;
- }
- else if (RequestHeader.class.isInstance(paramAnn)) {
- RequestHeader requestHeader = (RequestHeader) paramAnn;
- headerName = requestHeader.value();
- required = requestHeader.required();
- defaultValue = parseDefaultValueAttribute(requestHeader.defaultValue());
- annotationsFound++;
- }
- else if (RequestBody.class.isInstance(paramAnn)) {
- requestBodyFound = true;
- annotationsFound++;
- }
- else if (CookieValue.class.isInstance(paramAnn)) {
- CookieValue cookieValue = (CookieValue) paramAnn;
- cookieName = cookieValue.value();
- required = cookieValue.required();
- defaultValue = parseDefaultValueAttribute(cookieValue.defaultValue());
- annotationsFound++;
- }
- else if (PathVariable.class.isInstance(paramAnn)) {
- PathVariable pathVar = (PathVariable) paramAnn;
- pathVarName = pathVar.value();
- annotationsFound++;
- }
- else if (ModelAttribute.class.isInstance(paramAnn)) {
- ModelAttribute attr = (ModelAttribute) paramAnn;
- attrName = attr.value();
- annotationsFound++;
- }
- else if (Value.class.isInstance(paramAnn)) {
- defaultValue = ((Value) paramAnn).value();
- }
- else if (paramAnn.annotationType().getSimpleName().startsWith("Valid")) {
- validate = true;
- Object value = AnnotationUtils.getValue(paramAnn);
- validationHints = (value instanceof Object[] ? (Object[]) value :new Object[] {value});
- }
- }
- if (annotationsFound > 1) {
- throw new IllegalStateException("Handler parameter annotations are exclusive choices - " +
- "do not specify more than one such annotation on the same parameter: " + handlerMethod);
- }
- if (annotationsFound ==0) {// 若没有发现注解
- Object argValue = resolveCommonArgument(methodParam, webRequest); //判断WebRquest是否可赋值给参数
- if (argValue != WebArgumentResolver.UNRESOLVED) {
- args[i] = argValue;
- }
- else if (defaultValue !=null) {
- args[i] = resolveDefaultValue(defaultValue);
- }
- else {
- Class paramType = methodParam.getParameterType();
- if (Model.class.isAssignableFrom(paramType) || Map.class.isAssignableFrom(paramType)) {
- if (!paramType.isAssignableFrom(implicitModel.getClass())) {
- thrownew IllegalStateException("Argument [" + paramType.getSimpleName() +"] is of type " +
- "Model or Map but is not assignable from the actual model. You may need to switch " +
- "newer MVC infrastructure classes to use this argument.");
- }
- args[i] = implicitModel;
- }
- elseif (SessionStatus.class.isAssignableFrom(paramType)) {
- args[i] = this.sessionStatus;
- }
- else if (HttpEntity.class.isAssignableFrom(paramType)) {
- args[i] = resolveHttpEntityRequest(methodParam, webRequest);
- }
- elseif (Errors.class.isAssignableFrom(paramType)) {
- throw new IllegalStateException("Errors/BindingResult argument declared " +
- "without preceding model attribute. Check your handler method signature!");
- }
- elseif (BeanUtils.isSimpleProperty(paramType)) {// 判断是否参数类型是否是简单类型，若是在使用@RequestParam方式来处理,否则使用@ModelAttribute方式处理
- paramName = "";
- }
- else {
- attrName = "";
- }
- }
- }
- if (paramName != null) {
- args[i] = resolveRequestParam(paramName, required, defaultValue, methodParam, webRequest, handler);
- }
- else if (headerName != null) {
- args[i] = resolveRequestHeader(headerName, required, defaultValue, methodParam, webRequest, handler);
- }
- else if (requestBodyFound) {
- args[i] = resolveRequestBody(methodParam, webRequest, handler);
- }
- else if (cookieName != null) {
- args[i] = resolveCookieValue(cookieName, required, defaultValue, methodParam, webRequest, handler);
- }
- else if (pathVarName !=null) {
- args[i] = resolvePathVariable(pathVarName, methodParam, webRequest, handler);
- }
- else if (attrName != null) {
- WebDataBinder binder =
- resolveModelAttribute(attrName, methodParam, implicitModel, webRequest, handler);
- boolean assignBindingResult = (args.length > i +1 && Errors.class.isAssignableFrom(paramTypes[i +1]));
- if (binder.getTarget() !=null) {
- doBind(binder, webRequest, validate, validationHints, !assignBindingResult);
- }
- args[i] = binder.getTarget();
- if (assignBindingResult) {
- args[i + 1] = binder.getBindingResult();
- i++;
- }
- implicitModel.putAll(binder.getBindingResult().getModel());
- }
- }
- return args;
- }
private Object[] resolveHandlerArguments(Method handlerMethod, Object handler,
NativeWebRequest webRequest, ExtendedModelMap implicitModel) throws Exception {
Class[] paramTypes = handlerMethod.getParameterTypes();
Object[] args = new Object[paramTypes.length];
for (int i = 0; i < args.length; i++) {
MethodParameter methodParam = new MethodParameter(handlerMethod, i);
methodParam.initParameterNameDiscovery(this.parameterNameDiscoverer);
GenericTypeResolver.resolveParameterType(methodParam, handler.getClass());
String paramName = null;
String headerName = null;
boolean requestBodyFound = false;
String cookieName = null;
String pathVarName = null;
String attrName = null;
boolean required = false;
String defaultValue = null;
boolean validate = false;
Object[] validationHints = null;
int annotationsFound = 0;
Annotation[] paramAnns = methodParam.getParameterAnnotations();
for (Annotation paramAnn : paramAnns) {
if (RequestParam.class.isInstance(paramAnn)) {
RequestParam requestParam = (RequestParam) paramAnn;
paramName = requestParam.value();
required = requestParam.required();
defaultValue = parseDefaultValueAttribute(requestParam.defaultValue());
annotationsFound++;
}
else if (RequestHeader.class.isInstance(paramAnn)) {
RequestHeader requestHeader = (RequestHeader) paramAnn;
headerName = requestHeader.value();
required = requestHeader.required();
defaultValue = parseDefaultValueAttribute(requestHeader.defaultValue());
annotationsFound++;
}
else if (RequestBody.class.isInstance(paramAnn)) {
requestBodyFound = true;
annotationsFound++;
}
else if (CookieValue.class.isInstance(paramAnn)) {
CookieValue cookieValue = (CookieValue) paramAnn;
cookieName = cookieValue.value();
required = cookieValue.required();
defaultValue = parseDefaultValueAttribute(cookieValue.defaultValue());
annotationsFound++;
}
else if (PathVariable.class.isInstance(paramAnn)) {
PathVariable pathVar = (PathVariable) paramAnn;
pathVarName = pathVar.value();
annotationsFound++;
}
else if (ModelAttribute.class.isInstance(paramAnn)) {
ModelAttribute attr = (ModelAttribute) paramAnn;
attrName = attr.value();
annotationsFound++;
}
else if (Value.class.isInstance(paramAnn)) {
defaultValue = ((Value) paramAnn).value();
}
else if (paramAnn.annotationType().getSimpleName().startsWith("Valid")) {
validate = true;
Object value = AnnotationUtils.getValue(paramAnn);
validationHints = (value instanceof Object[] ? (Object[]) value : new Object[] {value});
}
}
if (annotationsFound > 1) {
throw new IllegalStateException("Handler parameter annotations are exclusive choices - " +
"do not specify more than one such annotation on the same parameter: " + handlerMethod);
}
if (annotationsFound == 0) {// 若没有发现注解
Object argValue = resolveCommonArgument(methodParam, webRequest); //判断WebRquest是否可赋值给参数
if (argValue != WebArgumentResolver.UNRESOLVED) {
args[i] = argValue;
}
else if (defaultValue != null) {
args[i] = resolveDefaultValue(defaultValue);
}
else {
Class paramType = methodParam.getParameterType();
if (Model.class.isAssignableFrom(paramType) || Map.class.isAssignableFrom(paramType)) {
if (!paramType.isAssignableFrom(implicitModel.getClass())) {
throw new IllegalStateException("Argument [" + paramType.getSimpleName() + "] is of type " +
"Model or Map but is not assignable from the actual model. You may need to switch " +
"newer MVC infrastructure classes to use this argument.");
}
args[i] = implicitModel;
}
else if (SessionStatus.class.isAssignableFrom(paramType)) {
args[i] = this.sessionStatus;
}
else if (HttpEntity.class.isAssignableFrom(paramType)) {
args[i] = resolveHttpEntityRequest(methodParam, webRequest);
}
else if (Errors.class.isAssignableFrom(paramType)) {
throw new IllegalStateException("Errors/BindingResult argument declared " +
"without preceding model attribute. Check your handler method signature!");
}
else if (BeanUtils.isSimpleProperty(paramType)) {// 判断是否参数类型是否是简单类型，若是在使用@RequestParam方式来处理,否则使用@ModelAttribute方式处理
paramName = "";
}
else {
attrName = "";
}
}
}
if (paramName != null) {
args[i] = resolveRequestParam(paramName, required, defaultValue, methodParam, webRequest, handler);
}
else if (headerName != null) {
args[i] = resolveRequestHeader(headerName, required, defaultValue, methodParam, webRequest, handler);
}
else if (requestBodyFound) {
args[i] = resolveRequestBody(methodParam, webRequest, handler);
}
else if (cookieName != null) {
args[i] = resolveCookieValue(cookieName, required, defaultValue, methodParam, webRequest, handler);
}
else if (pathVarName != null) {
args[i] = resolvePathVariable(pathVarName, methodParam, webRequest, handler);
}
else if (attrName != null) {
WebDataBinder binder =
resolveModelAttribute(attrName, methodParam, implicitModel, webRequest, handler);
boolean assignBindingResult = (args.length > i + 1 && Errors.class.isAssignableFrom(paramTypes[i + 1]));
if (binder.getTarget() != null) {
doBind(binder, webRequest, validate, validationHints, !assignBindingResult);
}
args[i] = binder.getTarget();
if (assignBindingResult) {
args[i + 1] = binder.getBindingResult();
i++;
}
implicitModel.putAll(binder.getBindingResult().getModel());
}
}
return args;
}RequestMappingHandlerAdapter中使用的参数绑定，代码稍微有些不同，有兴趣的同仁可以分析下，最后处理的结果都是一样的。
示例：
- @RequestMapping ({"/","/home"})
- public String showHomePage(String key){
- logger.debug("key="+key);
- return "home";
- }
@RequestMapping ({"/", "/home"})
public String showHomePage(String key){
logger.debug("key="+key);
return "home";
}
- @RequestMapping (method = RequestMethod.POST)
- public String doRegister(User user){
- if(logger.isDebugEnabled()){
- logger.debug("process url[/user], method[post] in "+getClass());
- logger.debug(user);
- }
- return "user";
- }
@RequestMapping (method = RequestMethod.POST)
public String doRegister(User user){
if(logger.isDebugEnabled()){
logger.debug("process url[/user], method[post] in "+getClass());
logger.debug(user);
}
return "user";
}这种情况下，就调用@ModelAttribute来处理。
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